Beware of thinking simpler is better. That's how you wind up pulling the engine entirely.

The difference from 140F to 180F should not be a fire risk, even paper won't catch until 451F and that's a long way off. Heating the boat, yes, that's something else again. Poor insulation, poor ventilation, and no blower can all contribute to that. Even at 140F, you may want to run the blower after the engine is shut down, so it cools off the boat AND so it cools off the engine and prevents the oil from coking.

Or just pull the engine.

That was one of the problems in the VW Beetle, by the way. Air cooled engine, terribly inefficient. Simple, yes, reliable, maybe, but very inefficient.